截面预裂的RC构件直剪与斜剪承载力比较

Comparison on the ultimate bearing capacities of direct shear and oblique shear for RC members with pre-cracked sections

钢筋混凝土构件截面中若存在与剪力方向平行的裂缝,则构件的直剪承载力显著降低。目前我国规范未进行直剪设计或验算,可能存在安全隐患。为说明此问题,进行了试验和分析研究。设计22个具有不同的贯通裂缝长度、直剪配筋率和直剪钢筋位置的Z形试件,得到了其直剪极限承载力。结果显示,直剪极限承载力随裂缝长度的增大而减小,但基本不受钢筋布置位置的影响。采用分析的方法并考虑可靠度近似一致,获得了与直剪面具有相同材料和几何特征但不同配箍率的构件斜剪极限承载力。在极限承载力和承载力设计值两个层面上,比较直剪和斜剪承载力。研究发现,若截面存在贯通裂缝、箍筋配筋率较大(大于0.18%)而直剪钢筋较少(小于0.60%)时,需要进行直剪承载力验算以保证设计安全。

The ultimate bearing capacities（ UBCs） of direct shear for reinforced concrete（ RC） members can be remarkably reduced due to the presence of the cracks parallel to the shear force.The current design codes in China do not provide an appropriate approach to design or check the UBCs of direct shear,which may have hidden danger.To demonstrate this irrationality,experimental and analytical studies were conducted.Twenty-two Z-shaped specimens with different crack lengths,reinforcement ratios and direct reinforcement positions were tested to obtain their UBCs of direct shear.The results show that the UBCs decrease when the crack lengths increase,but the UBCs of direct shear are not affected by the reinforcement positions.Considering the approximately identical reliability with the method of analysis,the UBCs of oblique shear with various stirrup ratios were obtained with the same material and geometric features as the direct shear specimens.By comparing the UBCs of direct shear with those of oblique shear in two perspectives of the ultimate bearing capacity and the design value of bearing capacity,it is found that the failure of direct shear occurs prematurely in certain situations of throughout cracking,stirrup ratio more than 0.18% and longitudinal reinforcement ratio less than0.60%.